A motor drive device described in Patent Literature 1 drives a motor by converting a DC voltage to an AC voltage by PWM control using switching of switching elements of an inverter circuit and by outputting the AC voltage to a motor coil. The motor drive device has a drive circuit portion which drives the switching elements by outputting an operation signal to the inverter circuit and a control portion which makes the switching elements switch by controlling the drive circuit portion by PWM. When the motor is stopped, the control portion performs a discharge control to discharge charges remaining in a smoothing capacitor of the inverter circuit. The motor drive device configured as above is installed to a vehicle, and power is supplied to the control portion from a low-voltage power supply, for example, at 12 V while power is supplied to the drive circuit portion from a high-voltage power supply, for example, at 200 to 400 V.